A fat tree is like a giant tree that helps computers and other devices talk to each other without problems. Imagine a tree that has many branches and leaves. At the bottom of the tree, there are many smaller branches that connect to other branches. These branches are like wires or cables that connect computers or other devices together. The branches get bigger as they go up the tree, like a bigger highway, so that information can travel faster and more easily.
Each branch connects to a computer or device, and all of the devices talk to each other through the branches. This way, all of the devices can share information and work together.
A fat tree is called this because it has many branches (like a "fat" tree) and it is designed to be very efficient and fast. It helps computers and other devices work together smoothly, like a big team.